The present invention relates to an inductive differential pressure sensor of the type comprising:
a rigid body delimiting an internal chamber; PA1 a flexible measuring diaphragm subdividing the chamber into two half chambers which are sealed from each other; PA1 means for applying two pressures to be compared to respective ones of the two half chambers, said pressures being applied directly or by means of a substantially incompressible hydraulic fluid, a central zone of the diaphragm being suitable for being displaced by a value representative of the value of the difference between the two pressures and along a reference direction perpendicular to a reference plane which is fixed relative to the body and which is defined by the general plane of the diaphragm when in its reference position; and PA1 electromagnetic means for measuring said displacement by induction. PA1 a magnetic core disposed in one or other of the two half chambers and fixedly mounted by means of a connection finger to the central zone of the diaphragm in such a manner that any displacement of the core in the reference direction is representative of the displacement of the central zone of the diaphragm; and PA1 two simple inductors fixedly mounted in the body around the magnetic core and juxtaposed in the reference direction, the dimensions and positions of the assembly being such that the further the magnetic core penetrates into one of the two inductors due to variation in the difference between the pressures to be compared, the further the core moves out from the other inductor; the difference between the two pressures to be compared thus being measured by the difference between the respective impedances, and preferably self inductances, of the two inductors. PA1 two identical magnetic cores are fixedly mounted on the central zone of the diaphragm and are symmetrically disposed on either side thereof in respective ones of the two half chambers, and are mutually aligned parallel to the reference direction; PA1 two identical simple inductors are fixedly mounted to the body in symmetrical positions on either side of the reference plane in mutual alignment parallel to the reference direction, each inductor being disposed about a respective one of the cores so as to present an impedance which is a function of the position of the core relative to the inductor; and PA1 electrical connection means for connecting the two inductors with means for determining the difference between their impedances; PA1 the body being at least partially symmetrical about the said reference plane.
Such sensors are used widely, and the Applicant sells one particular embodiment thereof under the reference number 6445.
In this particular embodiment, the electromagnetic measuring means comprise:
This embodiment is perfectly satisfactory so long as it is only required to operate under substantially constant predetermined temperature conditions.
Once the temperature begins to vary, variations are observed in the measurements due to the effect of temperature on the geometrical characteristics of the various portions of the sensor due to expansion, and on the magnetic and electrical characteristics of the assembly constituted by the core, the inductors, and in some cases the adjacent parts of the body of the sensor.
Preferred embodiments of the invention provide a structure for the electromagnetic measuring means which is suitable for ensuring automatic and permanent correction of the influence of temperature on the measurement zero, and this may be achieved without significantly increasing the size or the cost of the sensor.